This invention relates to an environmental control system, and, more particularly, to such a system with air conditioning apparatus controlled in accordance with both the condition of the environment being controlled and a predetermined timing sequence.
A common method for controlling the temperature within enclosures for growing birds, pigs or cattle has been to use temperature responsive thermostats, such as the type that employs Freon or other gas filled coils which expand or contract to actuate or deactuate air conditioning apparatus, such as ventilation louvers. Electronic thermostats for performing this condition responsive control are also known. Examples of these are shown in U.S. patent application Ser. No. 06/584,387 of Newell Jr. et al. entitled "Environmental Control System", filed Feb. 28, 1984, in U.S. patent application Ser. No. 06/584,398 of Newell III et al. entitled "Electronic Thermostat", filed Feb. 28, 1984 and in U.S. patent application Ser. No. 06/625,606 of Newell III et al. entitled "Thermostat", filed June 28, 1984, all of which are assigned to the assignee of the present application.
It is also known to use a cycle timer switch in combination with the gaseous tube-type thermostats which periodically actuate the air conditioning apparatus for a preselected portion of each preselected timing cycle. The duration of each cycle, or cycle period, and the portion of each cycle that the cycle timer switch actuates the air conditioning apparatus, or duty cycle, is selectively varied according to the age of the birds or other animals within the enclosure. This is necessary to optimize growth and health and to compensate for increase in body heat and other factors as the animals increase in size.
In the known control systems which employ cycle timers in combination with condition responsive controllers, actuation of the air conditioning apparatus by the cycle timer switch is completely independent of actuation by the condition responsive controller. Unfortunately, it is therefore not uncommon that the cycle timer will cause actuation of the air conditioning apparatus immediately after the end of actuation by the condition responsive controller. This results in excessive actuation of the air conditioning apparatus that causes energy waste and erratic and excessive temperature shifts.
Despite this problem, in the case of ventilation apparatus, the cycle timer switch control is considered necessary despite this problem to ensure adequate minimum ventilation. Guaranteed adequate minimum ventilation is needed for several reasons. In order to ensure safety and good health for the animals and workers in the enclosure, the gases and moisture caused by the products from combustion of otherwise unvented heating means and moisture and noxious gases produced from droppings and other litter must be eliminated and fresh oxygen replenished. During warm periods, it is also necessary to eliminate excess heat.
It is known in other types of environments to control condition responsive operation in accordance with a preselected timer sequence. For instance, in U.S. Pat. No. 4,431,130 of McInnes, a timer is used to disable a radiant heat selector for a preselected time period. Likewise, in U.S. Pat. No. 4,290,480 of Sulkowski, the operation of a multiphase environmental control system may be time sequenced to reduce performance on weekends.
While these known timers have been used in other environments to good advantage, they fail to overcome the disadvantages of known controllers for animal enclosures, as noted above. They lack a full range of control over the relative duration of actuation during each cycle period. Moreover, none of these ensure a minimum amount of actuation without reference to sensed conditions. They therefore fail to offer solutions to the problem of ensuring such minimum actuation while preventing excessive time sequenced actuation. As partly noted above, excessive actuation is wasteful of energy, interferes with accurate control of the environment, and has possibly harmful effects on the birds or other animals within the controlled environment.